The Scottish government is seeking a buyer for the Grangemouth oil refinery as staff prepare to find out whether the site's owner will follow through with a threat to shut it permanently amid a rancorous industrial dispute.

Grangemouth's owner, Ineos, has said it will consider a deal after the Scottish government made it clear it was looking for interest in the sprawling plant on the Firth of Forth.

The Switzerland-based chemicals giant, which shut the plant last week and has threatened to make the closure permanent, spent Tuesday considering its workforce's answers to an ultimatum on changes to terms and conditions. Ineos gave the refinery's 1,370 permanent workers until 6pm on Monday to respond to a "survival plan" for Grangemouth that would strip employees of their final salary pensions, freeze pay and cut other benefits.

With the Unite union claiming defeat for Ineos, the Scottish finance secretary, John Swinney, said he believed a buyer could be found for Grangemouth, which supplies 70% of Scotland's fuel and is a big contributor to its economy.

"I don't think it will come as any surprise to anyone that the government is looking for alternative options and there certainly will be other players around the globe interested in this particular plant," Swinney told the BBC's Good Morning Scotland programme."We have certainly had discussions with other players and the Scottish government will engage in any discussions that are helpful to ensure Grangemouth can continue to make a major contribution to the health and wellbeing of the Scottish economy."

Jim Ratcliffe, Ineos's billionaire chairman, and Calum MacLean, who runs Grangemouth, were unavailable for comment as they considered their options at an all-day meeting in London.

But Declan Sealy, a director of Ineos Grangemouth, said: "We are not different to any other business. We buy and sell businesses and assets all the time. This is a business that is financially distressed [but] we would be interested to talk to anybody interested in buying this site."

Ineos shut down Grangemouth last Wednesday even after Unite withdrew the threat of a 48-hour strike that would have started on Sunday. The company then put its demands to the workforce and threatened to leave Grangemouth idle permanently if its plan was rejected.

The company bypassed Unite by going straight to its workforce with cuts to staff costs it claimed were essential to give Grangemouth a future. MacLean said on Sunday the company had received about 300 acceptances but Ineos refused to give an update on Tuesday.

Unite said more than 680 of its members had rejected the plan. Officials said the total number of rejections would be substantially bigger and called for Ineos to withdraw its demands and return to talks.

Unite's Scottish secretary Pat Rafferty urged the Scottish parliament to hold an emergency debate on the security of the country's energy supply and the Scottish select committee at Westminster to hold an inquiry into Ineos's conduct.

"This site can't close. It's vital to the economy. It can't be left in the hands of one person," Rafferty said.

Sealy rejected Unite's assertion that employees who rejected the Ineos plan were the key workers needed to make the plant function. "Everybody who is working on this site has a key role. I don't accept Unite's comments there."

Ineos bought Grangemouth in 2006 from BP in what it said at the time was a transformational deal. But Ineos was hit badly by the global recession in 2008 and since then has tried to cut the generous benefits its workers inherited from BP. Swinney called on Ineos to reopen the plant so that discussions could resume. He said he accepted Unite's pledge that it would not strike for the rest of this year as long as the company withdrew its demands. Ineos said it would tell Grangemouth's workforce the result of its ultimatum on Wednesday.